Update README.rdoc

I think the binary releases are unnecessary these days [and harder due to the proliferation of versions of ruby] so just tell people to compile it theirselves on windows.
PR for issue#149, the rack middleware should create the print dir for profile result
Merge pull request #151 from zhougn/master

PR for issue#149, the rack middleware should create the print dir for pr...
updated CHANGES
bumped version to 0.15.2